1. Field of the Invention
The present invention relates generally to radar systems, and, more particularly, to a digital signal processing system for a ground-looking radar system.
2. Description of Related Art
A radar system, in its major elements, includes a radio frequency oscillator which is controlled by a pulse modulator, or pulser, so as to produce periodic high power electromagnetic energy pulses of relatively short duration. The pulses are applied to a highly directional antenna which transmits the pulses toward a target or towards a region in which a target is sought. A receiver, which may be interconnected with the same antenna as the transmitter, is controlled by a switching arrangement frequently referred to as a "duplexer" for interconnecting the antenna to the receiver during the interval between transmitted power pulses in order to receive reflected energy from a target. Monitoring antenna direction and timing of reflected pulse returns provides location and range of a target.
In what is referred to as a conical scan process, the radar beam is squinted and rotated about the antenna boresight. Targets located on boresight produce a constant signal return. For a target off boresight, the return signal is a modulated signal at the frequency of the beam rotation. The amplitude of the modulation indicates how far off boresight the target is, and return signal phase determines how far the target is off exact azimuth and elevation. In known systems, phase and quadrature reference signals are derived from the conical scan motor, and they are used to synchronously detect the return signal. The output of the two detection channels give the respective sine of the azimuth and elevation angles.
For a more detailed discussion of a conical scan radar system, reference can be made to Introduction to Radar Systems, by M. I. Skolnik, McGraw-Hill (1980), page 156.
There are other radar systems for detecting targets and their ranges which rely upon the radiation of unmodulated or continuous wave energy. The present invention, however, is not concerned with such continuous wave or "CW" radar systems, but rather with the aforedescribed pulse radar systems and, in particular, a conical scan radar system.